The mechanical linkages which govern the motion of present porch gliders are simple. An example of such a glider mechanism is found in U.S. Pat. No. 2,095,636. The porch glider is in essence intended as a substitute for the porch swing, used in situations where the long supports of a swing are neither practical nor desirable. An example of such is a location where there are no support structures above, from which to hang a swing.
The porch glider as a substitute for a porch swing has several shortcomings. The pivot arms from which a glider seat hangs define the path of motion of the glider. The pivot arms describe segments of circles as they pivot about the fixed mounting point at one end of each pivot arm. The radius of the circle is the distance between the fixed pivot point and the moving pivot point at either end of the pivot arm. The pivot arms of present porch gliders are considerably shorter than the radius of motion of a typical porch swing. Consequently the back and forth motion of the glider is accompanied by considerable, undesireable motion up and down. In the simplest glider designs, the pivot arms are arranged parallel to one another, and act as swings, describing circles of proportionally smaller radius than the motion of a porch swing. It is simply more work to move a given distance back or forth in a glider than in a swing.
Additionally, when a swing is in a position forward of the rest position it is tilted backwards, the further the travel the greater the backward tilt. Similarly, when the swing is in a position rearward of the rest position it is tilted forward. If the glider pivot arms are arranged parallel to one another then there will be no tilting of the glider chair in any position.
Many gliders are designed with the pivot arms arranged so that the fixed pivot points are further apart than the moving pivot points. That is, at each side of the glider, the pivot arms are further apart at top than at the bottom. An unfortunate consequence of this design is that the glider chair will tilt forward while forward of the rest position and the further the chair moves forward the greater the forward tilt. Similarly, motion of the glider chair rearward from the rest position will result in rearward tilting of the chair. This motion can be described as similar to that of a rocking chair, but it is exactly the opposite of the motion inherent in a swing.